Analysis of whirling motion for the dynamic system of floating ring seal and rotor

In turbopumps, the dynamic characteristics of the floating ring seal and rotor system are important, especially when the floating ring seal fails to lock up. To investigate the motion of the system with the unlocked floating ring seal, a dynamic model for the whirling system is established in this study. On the basis of the perturbation method, the nonlinear model is simplified into a steady whirling model superimposed with perturbation motion. The transient bulk flow model is improved to calculate the hydrodynamic force in the seal clearance. The results show that the floating ring seal is able to steadily follow the rotor whirling motion and reduce the rotor whirling amplitude when the friction is not enough to lock the seal. The perturbation motion is calculated and proved stable, as the direct rotordynamic coefficients of the floating ring seal are much larger than the cross-coupled coefficients. Further, the effects of the mass and the friction of the floating ring seal, the rotor whirling amplitude and the interaction between the seal and the rotor on the dynamic characteristics of the whirling system are investigated.